Supporting information for Schuck et al. (2003) Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0631579100
Table 1.
Relative concentrations of phosphatidylcholine (PC) species in detergent-resistant membranes (DRMs) from Madin-Darby canine kidney (MDCK) (A) and Jurkat cells (B). Total cell membranes (TCMs) and DRMs were obtained as before, and lipids were extracted and analyzed by mass spectrometry. Relative concentrations of all detectable species were calculated by using 13C-labeled lipids from Pichia pastoris as internal standards. Odd-numbered fatty acids presumably are of plant origin; they derive from the fetal calf serum used for cell culture and subsequently are incorporated into cellular phospholipids. The total amount of PC in the floating fraction of the TCMs represents an underestimate of total membrane PC as a sizeable fraction of membranes is lost during preparation, probably due to incomplete homogenization and adherence to nonfloating material such as nuclei, mitochondria, and the cytoskeleton. Because some weak detergents like Tween 20 prevent these losses without extensively solubilizing cell membranes, some DRMs can contain nearly as much as or even more PC than the TCMs.